Heart disease accounts for more deaths in the United States than any other disease. Sudden cardiac death (“SCD”) accounts for approximately 400,000 deaths and heart failure accounts for approximately 260,000 deaths annually in the United States. Most SCDs are caused by ventricular tachycardia (“VT”) or ventricular fibrillation (“VF”). Identifying patients at risk of SCD due to VT/VF remains a major challenge. Heart failure has also become a problem of epidemic proportions in the United States. Methods for tracking disease progression or regression may alert treating physicians as to who may benefit from additional therapies or changes in therapy.